1. Field of the Invention
This invention generally relates to null-balancing apparatus for measuring and controlling torque, and more specifically relates to the use of such apparatus for measuring fluid flow rate.
2. Background Information
Torque measurement is generally avoided in commercial products because of the difficulty in isolating the measurement means from the apparatus being measured. These limitations are the primary disadvantages of such means when applied to commercially available target flow sensors, which typically use a static strain gage arrangement to detect the torque produced by fluid impacting on a target.
Improved target meters have been disclosed by the inventor in his two current pending U.S. Patent Applications for moving target flow meters. One of these applications was filed on Apr. 1 2002 and has Ser. No. 10/113,411. The other of these applications was filed on Aug. 2, 2002, and has Ser. No. 10/211,211. Moreover, in his U.S. Pat. No. 5,948,978, entitled Induction Heated Mass Flow Sensor, the inventor has described an electromagnetic actuator (see FIGS. 4 and 4A therein) similar to that used in the present invention. The disclosures of U.S. Pat. No. 5,948,978, 10/113,411 and U.S. Ser. No. 10/211,211 are included herein by reference.
The invention provides null-balancing apparatus for measuring a rate of flow of a fluid impacting a vane fixedly attached to a vane shaft journaled within a housing. This apparatus preferably comprises a torque linking mechanism linking the vane shaft to a drive shaft arranged to be turned by a drive shaft actuator disposed within the housing and journaled within a yoke. The torque linking mechanism is carried by the yoke and arranged so that a first torque applied to either one of the drive the output shafts results in a second torque applied to the other of those two shafts, and so that the applied torque moves the yoke away from its selected normal setting. The apparatus also comprises a feedback control circuit; a position sensor for supplying an imbalance signal to the feedback control circuit responsive to the motion of the yoke away from its normal setting; a yoke actuator for supplying, under control of the feedback control circuit, a restoring force to the yoke to drive the yoke towards the normal setting; and a signal processor for deriving, from an electrical parameter representative of the restoring force, the rate of flow of the fluid impacting the vane.
In a preferred embodiment of the invention, the yoke position is sensed photoelectric displacement detector comprising two photodetectors illuminated with radiant energy from a single photoemitter so that a part of the yoke structure differentially blocks a portion of that energy reaching the photodetectors. The output from the photodetectors vary inversely corresponding to the offset of the yoke position from its initial straight alignment and their signals are used by an amplifier to power an electromagnet producing magnetic flux which acts on a pair of permanent magnets attached to the yoke in a feedback arrangement to restore the initial alignment
A preferred embodiment of the invention uses a gear train having three gears connected in series between a motor and its load. Both the motor drive shaft and the output load shaft are journaled for rotation within bearings fixed to a housing or other fixed support The drive shaft is also journaled within a yoke, and the shaft of the intermediate gear is journaled only with the yoke. In this arrangement, if unrestrained, the intermediate gear would tend to orbit around the motor gear. In the null-balancing measurement arrangement of the invention, however, the yoke position is electronically detected by a suitable position sensor and a correcting torque is applied by electromagnetic means to the yoke to maintain the normal meshed alignment of the gears. Electrical signals used to produce the correcting torque are a measure of the torque applied to the load gear.
Other embodiments of the invention provide for turning the output shaft through less than a complete revolution. In some such embodiments the torque linking mechanism comprises a rocker arm carried by a yoke that co-acts with axially oriented eccentric drive pins mounted on rotating elements fixedly attached to the drive and output shafts.
In another embodiment of the invention, a Hall effect magnetic sensor detects the magnetic flux from the two permanent magnets. This sensor signal is also used with an amplifier to power an electromagnet which acts on the two permanent magnets attached to the yoke to restore the initial straight alignment.
In a further embodiment, the output shaft is used to rotate a vane in a fluid stream so that the torque measurement resulting from the effects of the fluid flow on the vane is used to provide a measure of the fluid flow rate. Thus, it is a particular object of this invention to provide an improved means for measuring torque and in particular, to apply that to target flow meters.
In some embodiments the drive shaft actuator is not an ordinary electric motor, but comprises an electromagnet that co-acts with a pair of oppositely poled permanent magnets eccentrically attached to a drive disk that is fixedly attached to the drive shaft.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the features and advantages may be provided by some embodiments.